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벌크 비정질 합금 고온 변형과 구조 완화의 상관관계 고찰
윤동현(D. H. Yoon),이광석(K. S. Lee) 한국소성가공학회 2010 한국소성가공학회 학술대회 논문집 Vol.2010 No.10
Effects of both isothermal annealing and warm deformation upon the structural relaxation behavior of Zr₄₄Ti₁₁Cu9.8Ni10.2Be₂? (LM1B) bulk metallic glass (BMG) were investigated. By utilizing structurally relaxed but not yet crystallized samples, which were obtained from bulk-to-bulk warm extrusion introducing different amount of free volume annihilation, we employ precise density measurement as well as differential scanning calorimetry to study free volume changes closely associated with the degree of structural relaxation. Isothermal annealing within supercooled liquid region (SLR) generates the annihilation of free volume by ~0.1%, and in-situ deformation little more promotes this annihilation process. Contrary to classical concept of annealing-induced embrittlement due to the reduction of free volume and subsequent densification, it is interesting to note that the sample relaxed at the mid-temperature within SLR (673 K for LM1B) exhibits additional plastic strains compared with as-received counterpart.
저열팽창 Ni<SUB>x</SUB>Fe<SUB>100-x</SUB> (x=36, 40, 44) 합금의 고온 변형 거동
윤동현(D. H. Yoon),이광석(K. S. Lee),정중은(J. E. Jung),장영원(Y.W. Chang),이정환(J.H. Lee) 한국소성가공학회 2011 한국소성가공학회 학술대회 논문집 Vol.2011 No.10
In this study, high temperature deformation behavior of low thermal expansion coefficient NixFe100-x (x=36, 40, 44) alloys was investigated at temperature ranging from 600 to 1200 ℃ at the strain rates between 10<SUP>-4</SUP> and 10<SUP>0</SUP> /s by conducting a series of compression tests. Both the temperature and strain rate dependence of the flow stress can be described via the hyperbolic sine function together with microstructural characterization. Based on the results, the empirical deformation map was also constructed, from which the contour conformed to high power dissipation efficiency could be exhibited as the feasible processing combination for each alloy.
STS-Al-Mg 3-ply 이종금속소재 계면 미세 조직 및 변형 특성에 미치는 열처리의 영향
이광석(K.S. Lee),조유미(Y.M. Jo),윤동현(D.H. Yoon),이수은(S.E. Lee),허진희(J.H. Heo),강남현(N.H. Kang),권용남(Y.N. Kwon),이영선(Y.S. Lee) 한국소성가공학회 2012 한국소성가공학회 학술대회 논문집 Vol.2012 No.10
We present here an exploration of the relationship among post-roll bonding process variables, interfacial and overall mechanical properties of a 3-ply STS-Al-Mg laminated composite. The effect of post-annealing conditions upon the evolution of interface microstructure is first analyzed by means of optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) attached with energy dispersive spectroscopy (EDS). Taking the composition and thickness of each intermetallic compound layer into account, results devoted to the interfacial microstructure and overall mechanical properties are also given. Local mechanical properties for the generated diffusion layers were first determined by nanoindentation tests. The mechanism of improvement of interfacial bonding is then verified by means of uniaxial tensile and bending tests. Finally the competitions between two contradictory effects, viz., interface strengthening by the generation of IMCs and the corresponding loose of overall ductility due to the embrittlement, is discussed.